1. Field of the Invention
This invention relates generally to the development of interactive visual media, and, more specifically, to the generation of a set of files representing “zoomed-in” sections of a master high-resolution image file and the generation of the logical data required to allow navigation of the generated files.
2. Background Information
Within the field of this invention, visual media are media that are capable of presenting motion or still images to a viewer on a display such as a television screen or a computer monitor. “Interactive” visual media are distinct from “linear” or “passive” visual media because they allow the timing, order, and conditions governing presentation to vary depending on input from the end-user (the viewer).
Since the advent of the Compact Disc in the early 1980s, a wide range of CD-based interactive media have been developed and marketed, including CD-i, Video CD, Super Video CD, and a variety of CD-ROM formats intended for playback in computer-hosted CD-ROM drives. More recently, interactive visual media have been based on the DVD format as well, including DVD-Video and DVD-Audio. Programs with the same interactive characteristics may also be played back from a computer hard drive, either locally or from a server over a data or telephone network, and viewed in either a dedicated application or a general-purpose viewer such as an Internet browser.
In a typical interactive playback setting, user input is communicated to the playback device via a remote control or a computer mouse and keyboard. The user responds to on-screen prompts or menus (lists of possible options) by pressing keys or clicking the mouse. The playback path through the material available to be played is altered according to the choices or “navigation” of the user.
When presenting interactive visual media, a playback device works with two basic categories of data to create the experience of the end-user. Presentation data is the data that is actually seen or heard: the video, audio, graphics and text. Logical data is information about the order and conditions under which presentation data is presented. Logical data defines the way the content is organized, and also the way in which user input will affect the navigational flow through the presentation data.
The creation of interactive visual media is referred to as “authoring,” that is generally accomplished using one or more software applications running on a computer. Logical data is generated to structure the playback of the presentation data, to define the “user interface” (e.g. menus) used to navigate the program, to define the choices offered to users during playback, and to define the response of the playback device to user input. The logical data created in authoring takes the form of files that can be read and interpreted by a playback device designed to play back the media format being authored.
Presentation data, meanwhile, is put into a form, such as a specific file format, that is playable by the target playback device. One of the types of presentation data used in interactive visual media is still images. Still images are frequently used as the background for menus, and may also be arranged into sequences displayed in a manner analogous to slides in a slide projector. The DVD-Video specification, for example, supports two types of still image presentations: Slide Shows, using finite cell still or a finite presentation time in which the duration of each image is predetermined, and Still Shows, using infinite cell still or VOBU still in which user input controls the timing of the progression from one image to the next. More information is given in the DVD Specification for Read-Only Disc, Part 3, Video Specification, version 1.0, © 1996, DVD Forum, which is hereby incorporated by reference, and in particular in Section 3.3.6.4, Still and Pause. 
The specific form into which a still image is converted during authoring varies depending on the requirements of the interactive visual format that is being authored. Since such formats work with digital presentation data, however, the image generally must be digitized (if it was not originally acquired or created in digital form), scaled to the resolution at which it will be used in the finished program, and converted to a file format supported by the authoring software.
In digital images, the resolution is expressed as the number of horizontal pixels (the smallest point on the screen that may be individually addressed by the display device) by the number of vertical pixels (e.g. “640×480”). The proportion of the horizontal to the vertical is referred to as the “aspect ratio” (e.g. 4:3, the aspect ratio of the typical television screen). Resolutions that are close to the nominal resolution of a standard television set are often thought of as being normal or standard. Images with significantly greater resolution are thought of as being “high resolution.”
Digital images may be created in a digital image processing program, shot on conventional film and scanned (digitized), or shot with a digital camera. In any of these cases, the images commonly exist at a high resolution. Many interactive visual media, however, only support playback of images at normal resolution. When prepared for incorporation into such media, images are scaled during authoring. As a result of this scaling, much of the data from the high-resolution image is no longer present in the prepared image as the highest native resolution of the format is lower than the original resolution of the image.
Many viewers of interactive media would like to be able to “zoom in” on a still image for a magnified view of certain areas of the full image. For instance, zooming in on the upper left of a 640×480 image might involve taking a 160×120 subsection of the full image and expanding it so that it fills 640×480 pixels. In this type of scaling, however, a single pixel in the original image would be represented in the scaled display by a 4×4 block of pixels of the same color-value. The result of this approach to zooming is substantial degradation in the apparent image quality in the zoomed-in view, with artifacts (“blockiness”) that are apparent even to the untrained eye. In other words, the on-screen size of the zoomed-in section is greater than it was in the full (un-zoomed) image, but the visual information (detail) available to the viewer remains the same.